1. Field of Invention
The present invention relates to a process for using electromagnetic energy in the radiofrequency region to catalyze with char to perform selective chemical reactions involving oxides.
2. Background
Many major industrial operations produce selected gases, often in the form of polar molecules or molecules that absorb readily upon char, that need cleanup or conversion to more environmentally mundane materials. Conventional chemical processing requires much energy, since the heats of reaction are often high.
Coal is a major energy resource of the United States and must be utilized in increased amounts if energy independence is potentially a viable goal. A major problem associated with coal combustion is the resulting emissions of sulfur dioxide (SO.sub.2) and nitrogen oxides (NO.sub.x) into the atmosphere. Current flue gas removal technologies are not only expensive and cumbersome, but also produce troublesome waste products. High volumes of chemicals currently are required for SO.sub.2 removal while NO.sub.x removal often uses expensive platinum catalysts. High conversions remain a difficult goal for these current technologies for the convenient chemical reactions require high activation energies, and thus, normally high temperatures.
Current converters to further react CO, NO.sub.x, and soot from vehicle exhausts is expensive and often inefficient. Many industrial chemical operations produce H.sub.2 S and this must be reacted into other forms before any release to the environment.
Quantum radiofrequency (RF) physics is based upon the phenomenon of resonant interaction with matter of electromagnetic radiation in the microwave, RF regions since every atom or molecule can absorb, and thus radiate, electromagnetic waves of various wavelengths. The detection of the radiated spectrum to determine the energy levels of the specific atoms or molecules is called radiofrequency spectroscopy. Often the so called "fine lines" are of interest, and these are created by the rotational and vibrational modes of the electrons. For instance, refer to L. Stepin, Quantum Radio Frequency Physics, MIT Press, 1965.
In the subject invention, the inverse is of interest, that is the absorption of microwave, RF wavelengths by the energy bands of the atoms or molecules resulting in a heating of the nonplasma material and the excitation of valence electrons. This lowers the activation energy required for desirable chemical reactions. In this sense, RF energy itself is often described as a type of catalysis when applied to chemical reaction rates. For instance, refer to Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd Edition, Volume 15, pages 494-517, Microwave Technology.
The electromagnetic frequency spectrum is conveniently divided into ultrasonic, microwave, and optical regions. The microwave region runs from 300 MHz (megahertz) to 300 Ghz (gigahertz) and encompasses frequencies used for much communication equipment. For instance, refer to N. Cook, Microwave Principles and Systems, Prentice-Hall, 1986. A narrow part of this microwave region, 915 to 5000 MHz, is commonly employed for selective heating purposes. Microwave ovens are a common household item and operate normally using 2450 MHz, which is a good frequency for exciting water molecules. Because many vibrational energies are involved from a series of molecules for many applications involving mixtures, the actual radiofrequency energy employed is not critical from a frequency viewpoint; thus, the total practical range of from 915 to 5000 MHz is equally effective in catalyzing chemical reactions of mixtures. For instance, refer to Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd Edition, Volume 15, pages 494-517, Microwave Technology.
Some authors refer to "tuning" to one directed frequency for a given molecular bond response. Yet a more practical situation for mixtures nothing prevents the RF frequency from changing in a given manner, such as continuously over a range or in time steps. In most circumstances where a mixture of molecules is present sufficient excitation can be obtained by any set frequency in the normal range of 915 to 5000 MHz sometimes by increasing the power.
Because of cost many commercial as well as industrial microwave heating units operate at 2450 MHz, and this frequency is normally employed; however, as scale-up of equipment occurs, wave guide design often makes it more efficient to shift to the 915 MHz frequency.
This type of microwave heating often goes by the common name "RF Heating" and is actually a misnomer for most actual radiofrequencies lie in the what is now called the ultrasonic region. This concept of using the symbol RF to indicate a catalytic heating action for chemical reactions, regardless of the actual frequencies employed, is common.
Much energy related research was performed in the decade of the 1970s, and a number of United States patents were issued. These and others include:
______________________________________ No. Inventor Year ______________________________________ 3,502,427 Johswich 1970 3,565,777 Lauer 1971 3,656,441 Grey-1 1972 3,765,153 Grey-2 1973 3,869,362 Machi-1 1975 3,887,683 Abe 1975 3,960,682 Baranova 1976 3,981,815 Taniguchi 1976 3,997,415 Machi-2 1976 4,004,995 Machi-3 1977 4,076,606 Suzuki 1978 4,076,607 Zavitsanos 1978 4,175,016 Lewis 1979 4,435,374 Helm 1984 4,940,405 Kelley 1990 ______________________________________
Referring to the above list, Johswich discloses an acid treated activated carbon, giving a higher porosity, for use in removing sulfur, sulfur oxides and nitrogen oxides from flue gases. Lauer discloses a process to decompose sulfur dioxide by first electrically charging water used for absorption and then exposing to an ultraviolet light catalyst to enhance sulfur formation. Grey-1 discloses a cyclone wall-film wash for flue gas components that is enhanced by an electrostatic corona discharge. Grey-2 discloses equipment for an electrostatic ionizing process within a cyclone system that removes flue gas components.
Machi-1 discloses a process for removing SO.sub.2 and NO.sub.x by employing ionizing radiation or ultraviolet light at specific compositions to enhance their decomposition. Abe discloses a process for the removal of nitrogen oxides by injecting ammonia and absorbing on activated charcoal with a vanadium oxide catalyst. Baranova discloses a process for handling waste gas containing sulphurous-acid anhydride using an inorganic manganese salt as catalyst. Taniguchi discloses a process for removing sulfur dioxide and nitrogen dioxides by using ionizing radiation to form a removable aerosol.
Machi-2 discloses an improvement over Machi-1 by employing contaminated air as part of the process. Machi-3 discloses an improvement over Machi-1 by employing high dose rate electron beam irradiation. Suzuki discloses a process for decomposing NO.sub.x using microwave irradiation in the presence of normal exhaust gas constituents, such as SO.sub.2, CO.sub.2, in a typical homogenous decomposition.
Zavitsanos discloses a process for partially removing sulfur from coal by in-situ reactions using standard microwaves. Lewis discloses a radiolytic-chemical process for gas production employing nitrogen oxides to inhibit secondary reactions.
Helm discloses a high temperature process employing superheated steam with carbon and microwave irradiation to produce water gas. Kelley discloses a two stage furnace pulsed combustor where the first combustor forms soot that is employed to reduce SO.sub.2 and NO.sub.x in the second combustor where calcium is added to react with the sulfur.
Microwave heating was employed in other activities. For instance, Wall et al retorted oil shale with a standard microwave source in "Retorting Oil Shale by Microwave Power," 183 Advances in Chemistry Series 329, American Chemical Society, 1979.